Method of operating a blast furnace



United States Jersey No Drawing. Filed Oct. 7, 1960, Ser. No. 61,064

2 Claims. (CI. 75-42) This invention relates to a method of operating ablast furnace and more particularly to the production of iron in whichgaseous hydrocarbons are substituted for part of the coke ordinarilyused. Many attempts have been made to reduce the amount of coke requiredin this manner. These methods were generally of two types; one in whichthe hydrocarbons were burned with air and/ or oxygen and the products ofcombustion then introduced into the blast furnace and the second inwhich the hydrocarbons were directly introduced into the tuyere zone ofthe blast furnace. To the best of our knowledge none of these attemptswere successful. We believe that the failure of these attempts was-dueto the failure to properly modify the coke charge and the temperature ofthe hot blast to compensate for the chilling effect of the hydrocarbons.In the presence of coke, hydrocarbons do not release suflicient' heatinto the furnace to maintain the temperature normally present in thetuyere zone of the blast furnace. Thus, the priorpractices resulted in aloss of production.

It is therefore an object of our invention to provide a method ofoperating a blast furnace in which the coke charge and the temperatureof the hot blast are so controlled as to produce pig iron efficiently.

This and other objects will be more apparent after referring to thefollowing specification.

Assuming that the blast furnace is operating in a conventional methodits operation will be modified in the following manner: From 2 to 6hours before the injection of the hydrocarbons the coke charged per tonof hot metal is reduced and the hot blast temperature is raised.Specifically the usual coke charged per ton of hot metal is decreased byan amount equal to 0.8 to 1.0 mole of contained carbon in the coke foreach mole of carbon in the injected hydrocarbons plus an amount equal to0.2 to 0.4 mole of contained carbon for each mole of hydrogen in theinjection hydrocarbons. The hot blast temperature is raised from 30 to60 F. above the normal operating temperature (usually between 1000 F.and 1600 F. in conventional blast furnaces) for each mole of carbonremoved from the coke per ton of hot metal on account of the injectedhydrocarbons. The coke charged per ton of hot metal is then furtherreduced by an amount equal to 1.66 to 4.16 moles of contained carbon foreach 100 F. increase in the hot blast temperature. The hydrocarbons arepreferably injected through every tuyere of the furnace to eliminatelocalized chilling. If desired, /2 mole of high purity oxygen may beinjected into the furnace per mole of carbon in the added hydrocarbons.

The coke rate and blast temperature achieved at the end of thetransition period are maintained as long as the hydrocarbons are beingintroduced into the furnace.

In one particular procedure in which iron was produced in anexperimental blast furnace having a 4 foot diameter hearth, a 20 footstack and a 39 inch bosh, the furnace was operated with the burdenconsisting of sinter, coke, limestone, dolomite and gravel having thefollowing analyses:

atent ice Sinter Coke Limestone Dolo- Gravel mite Fixed C 91. 1

It will be understood that the iron containing component may be ordinaryore, sintered ore or flue dust or any other conventional charge. Theterm iron ore will be used hereinafter to designate any of these ironbearing constituents. When operating the furnace without hydrocarboninjection the furnace was operated with a sinter to coke ratio of 2.3and an oxidizing blast (including moisture) of 984 standard cubic ft.per minute at a temperature of 1730" F. The hot blast temperature wassubstantially higher than in a conventional blast furnace because of itssmall size with resultant high heat loss. A production rate of 1806 lbs.of hot metal per hour was obtained and 1336 lbs. of coke were consumedper ton of hot metal produced. When operating the furnace with ahydrocarbon injection (in the form of methane or natural gas) ofapproximately 38.3 cubic ft. per minute and a total blast of- 968.3cubic ft. per minute at a hotblast temperature of 2014 F. a productionrate of 1832 lbs. of hot metal per hour was obtained. The coke rate wasreduced to 1117 lbs. of coke per ton of hot metal. The following tablegives a comparison of the average operating data without hydrocarboninjection and with 4% methane injection.

TABLE II Comparison of Average Operating Data During Base Period and 4%Methane In ection Without With hydrohydrocarbon carbon 1. Dry Blast Air(5.0.1111) 978. 1 924. 4 2. Ambient Moisture in blast (s.c.f.m.)- 5. 95. 6 3, Methane Injected in blast (s.o.f.m.) 38. 3 4. Total Wet Blast(s.c.f.m.) 984 968.3 5. Average Hot Blast Temp. F.) 1, 730 2,014 6. TopGas Analysis (dry):

CO 30. 2 27. 3 CO2 12. 1 12. 6 H2 0. 8 4. 4 N2 56. 3 55. 1 7. Top GasVolume (sci. 1,375 1,312 8. Top Gas Temperature 592 644 9. ProductionRate (lb. h.in./hr 1,806 1,832 10. Coke Rate (1b. eoke/t.h.m.) 1,3361,117 11. Slag Volume (lb./t.h.m.) 573 669 12. Percent Si in metal 0. 860. 13. Percent S in rnetal 0.041 0.028 14. Hot Metal Temp. F 2, 4202,413 15. Slag Temp. F.) 2,691 2,680

In arriving at the above operation it was first decided that the totalblast should remain approximately constant and that the hydrocarbonaddition should be approximately 4% of the wet air blast which wasassumed to be 935 cu. ft. per minute. On this basis the hydrocarbonaddition was calculated to be 2244 cu. ft. per hour. With a productionrate of 1806 lb. per hour the hydrocarbon addition per ton of hot metalwas calculated to be or 2480 cu. ft. at atmospheric pressure and 60 F.The number of moles of CH; is equal to correspondingly this resulted in6.54 moles of carbon and 13.08 moles of hydrogen. On the basis of 0.8mole of contained carbon per mole of carbon in the methane and 0.2 moleof contained carbon per mole of hydrogen in the methane the amount ofcarbon decrease per ton of hot metal was calculated to be 0.8 6.54+0.213.08 or 7.85 moles. n the basis of raising the desired blasttemperature 40 F. per mole of carbon removed the desired blasttemperature was calculated to be or 2044 F. It was decided to furtherreduce the amount of coke by an amount equivalent to 1.70 moles ofcontained carbon per 100 F. increase in blast temperature. This amountedto 5.34 moles. On this bases the total reduction in coke per ton of hotmetal amounted to (7.85+5.34) 12+.91 or 174 lbs. With the foregoing asthe basis for the changes in operating conditions the coke rate waslowered and the blast temperature was raised. Minor changes were made inthe burden and blast temperature as are common in the operation of blastfurnaces to obtain best operating conditions. As a result it wasdetermined that the furnace worked best under the conditions set forthin Table II.

When oxygen is injected it is preferred to add the oxygen directly tothe oxidizing blast. The use of oxygen increases the production rate.

While one embodiment of our invention has been shown and described, itwill be apparent that other adaptations and modifications may be madeWithout depart ing from the scope of the following claims.

We claim:

1. The method of operating a blast furnace which comprises chargingcoke, limestone and iron ore into the top of the furnace, introducinghydrocarbons and an oxidiz- 5 ing blast into the furnace at the tuyeres,reducing the amount of coke charged from that normally used withouthydrocarbon addition, the amount of coke reduction per ton of hot metalproduced being equal to between 0.8 and 1.0 mole of contained carbon permole of carbon in said hydrocarbons plus 0.2 to 0.4 mole of containedcarbon per mole of hydrogen in said hydrocarbons, raising the blasttemperature above normal between 30 F. and 60 F. per each mole of carbonin the said coke decreased per ton of hot metal, and further reducingthe amount of coke per ton of hot metal an amount equal to 1.66 to 4.16moles of contained carbon per 100 F. increase in the oxidizing blasttemperature.

2. The method of operating a blast furnace according to claim 1 in whichthe oxidizing blast includes air enriched with oxygen, the amount ofoxygen being at least approximately /2 mole per mole of carbon in saidhydrocarbons.

References Cited in the file of this patent UNITED STATES PATENTSKendall May 25, 1886 Kinney May 13, 1947 Pomykala Sept. 27, 1955 RaickDec. 20, 1955

1. THE METHOD OF OPERATING A BLAST FURNACE WHICH COMPRISES CHARGINGCOKE, LIMESTONE AND IRON ORE INTO THE TOP OF THE FURNACE, INTRODUCINGHYDROCARBONS AND AN OXIDIZING BLAST INTO THE FURNACE AT THE TUYERES,REDUCING THE AMOUNT OF COKE CHARGED FROM THAT NORMALLY USED WITHOUTHYDROCARBON ADDITION, THE AMOUNT OF COKE REDUCTION PER TON OF HOT METALPRODUCED BEING EQUAL TO BETWEEN 0.8 AND 1.0 MOLE OF CONTAINED CARBON PERMOLE OF CARBON IN SAID HYDROCARBONS PLUS 0.2 TO 0.4 MOLE OF CONTAINEDCARBON PER MOLE OF HYDROGEN IN SAID HYDROCABONS, RAISING THE BLASTTEMPERATURE ABOVE NORMAL BETWEEN 30*F. AND 60*F. PER EACH MOLE OF CARBONIN THE SAID COKE DECREASED PER TON OF HOT METAL, AND FURTHER REDUCINGTHE AMOUNT OF COKE PER TON OF HOT METAL AN AMOUNT EQUAL TO 1.66 TO 4.16MOLES OF CONTAINED CARBON PER 100*F. INCREASE IN THE OXIDIZING BLASTTEMPERATURE.